oEmbed: Fix PHP warnings when a registered provider is malformed #35271

Job	Run time
Determine Matrix	3s
Single Site Default / Test before	14m 6s
Multisite Memcached / Test before	14m 46s
Single Site Memcached / Test current	14m 5s
Multisite Memcached / Test current	13m 2s
Single Site Default / Test current	13m 14s
Multisite Default / Test current	14m 10s
Single Site Memcached / Test before	13m 41s
Multisite Default / Test before	13m 47s
Compare / Single Site Memcached	12s
Compare / Multisite Memcached	15s
Compare / Single Site Default	20s
Compare / Multisite Default	11s
Slack Notifications	0s
Failed workflow tasks	-1s
	1h 51m 51s

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